Flexible endoluminal stent and process of manufacture

ABSTRACT

A generally tubular intraluminal compound stent comprising a plurality of component stents, each component stent having a length and a plurality of individual hoops axially disposed along the length and connected by a connecting spine, the component stents meshed with one another such that at least one hoop of one component stent is positioned between axially adjacent hoops of another component stent. The connecting spines may be helical, with at least one component stent spine oriented in a different helical direction than the spine of another component stent. Each hoop may further have a periphery comprising a pattern of zig-zags having apices, wherein adjacent hoops of the meshed component stents are aligned such that the apices of adjoining hoops abut or are interdigitated with one another. The compound stent may further comprise connectors, such as sutures, connecting at least some of the abutting or interdigitated apices. A process for manufacture of a flexible endoluminal compound stent is also disclosed.

TECHNICAL FIELD

The present invention relates generally to endoluminal grafts or“stents” and, more specifically, to a flexible stent advantageous foruse in a curved or tortuous lumen.

BACKGROUND OF THE INVENTION

A stent is an elongated device used to support an intraluminal wall. Inthe case of a stenosis, a stent provides an unobstructed conduit forblood in the area of the stenosis. An intraluminal prosthesis maycomprise a stent that carries a prosthetic graft layer of fabric. Such aprosthesis may be used, for example, to treat a vascular aneurysm byremoving the pressure on a weakened part of an artery so as to reducethe risk of rupture. Typically, an intraluminal stent or prosthesis isimplanted in a blood vessel at the site of a stenosis or aneurysmendoluminally, i.e. by so-called “minimally invasive techniques” inwhich the stent, restrained in a radially compressed configuration by asheath or catheter, is delivered by a stent deployment system or“introducer” to the site where it is required. The introducer may enterthe body through the patient's skin, or by a “cut down” technique inwhich the entry blood vessel is exposed by minor surgical means. Whenthe introducer has been threaded into the body lumen to the stentdeployment location, the introducer is manipulated to cause the stent tobe ejected from the surrounding sheath or catheter in which it isrestrained (or alternatively the surrounding sheath or catheter isretracted from the stent), whereupon the stent expands to apredetermined diameter at the deployment location, and the introducer iswithdrawn. Stent expansion may be effected by spring elasticity, balloonexpansion, or by the self-expansion of a thermally or stress-inducedreturn of a memory material to a pre-conditioned expanded configuration.

Some locations in which stents may be implanted are tortuous in nature,such as the aortic arch for thoracic aneurysm treatment. Additionally,the aneurysm may gradually change in volume after implantation of thestent (known in the art as D3 and H3 shrinkage). Known stents may not beflexible enough to adjust to the tortuosity of the lumen along itslength or to changes in the aneurysm after implantation. Thus, it wouldbe useful to have a more flexible stent to accommodate such situations.

SUMMARY OF THE INVENTION

The present invention comprises a generally tubular intraluminalcompound stent comprising a plurality of component stents, eachcomponent stent having a length and a plurality of individual hoopsaxially disposed along the length and connected by a connecting spine.The component stents are meshed with one another such that at least onehoop of one component stent is positioned between axially adjacent hoopsof another component stent. Each component stent may comprise a singlewire, each hoop comprising a circumferential winding of the wire, andthe connecting spine comprising at least one connecting spine membercomprising an extension of the wire between adjacent hoops. Eachconnecting spine may traverse each component stent circumferentially ina helical pattern, wherein the spine of at least one component stent isoriented in a different helical direction than the helical direction ofthe spine of another component stent in the compound stent. The compoundstent may consist essentially of a first component stent having a firstconnecting spine and a second component stent having a second connectingspine. The hoops of the first component stent may be axiallyinterspersed with the hoops of the second component stent in analternating pattern, such as a single hoop alternating pattern. Thefirst connecting spine may be helically oriented in a clockwisedirection and the second connecting spine oriented in acounter-clockwise direction.

Each hoop may further have a periphery comprising a pattern of zig-zagshaving apices, wherein adjacent hoops of the meshed stents are alignedsuch that the apices of adjoining hoops abut or are interdigitated withone another. The compound stent may further comprise connectors, such assutures, connecting at least some of the abutting or interdigitatedapices.

The invention also comprises a process for manufacture of a compoundstent having a length, the method comprising creating a plurality ofcomponent stents, each component stent having a length and a pluralityof hoops axially disposed along the length and connected by a connectingspine. The process comprises meshing the plurality of component stentstogether such that at least one hoop of one component stent ispositioned between axially adjacent hoops of another component stent.Each hoop of each stent may further comprise a pattern of zig-zagshaving apices in which case the method further comprises meshing thecomponent stents so that the apices of adjacent hoops of the meshedcomponent stents abut or are interdigitated with one another. Theprocess may further comprise connecting at least some of the abutting orinterdigitated apices with one another. Creating each component stentmay comprise creating each component stent by winding a single wirecircumferentially to form each hoop and extending connecting spinemembers between adjacent hoops, aligning the connecting spine memberssuch that the connecting spine members collectively form a connectingspine oriented in a helical pattern. In such case, the process furthercomprises creating at least one of the component stents with aconnecting spine that traverses the component stent in a helicalorientation opposite the helical orientation of the connecting spines ofthe other component stents, so that meshing the component stentstogether comprises crossing the oppositely-oriented helical spines in atleast one location along the compound stent.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, but are notrestrictive, of the invention.

BRIEF DESCRIPTION OF DRAWING

The invention is best understood from the following detailed descriptionwhen read in connection with the accompanying drawing. It is emphasizedthat, according to common practice, the various features of the drawingare not to scale. On the contrary, the dimensions of the variousfeatures are arbitrarily expanded or reduced for clarity. Included inthe drawing are the following figures:

FIGS. 1A and 1B are end and side views, respectively, of an exemplaryfirst component stent of the present invention in isolation.

FIGS. 2A-2B are end and side views, respectively, of an exemplary secondcomponent stent of the present invention in isolation.

FIG. 3 is a side view illustration of an exemplary compound stent of thepresent invention comprising the component stents of FIG. 1B and FIG. 2Bmeshed together.

FIGS. 4A-4C are schematic side view illustrations of the exemplarycompound stent of FIG. 3 in a flexed configuration viewed along an innerradius of curvature, showing differing amounts of overlap betweensuccessive hoops at varying radii of curvature.

FIG. 5 is a flowchart depicting an exemplary process for manufacture ofa stent of the present invention.

DETAILED DESCRIPTION OF INVENTION

Referring now to the drawing, FIGS. 1A-4 illustrate various aspects ofan intraluminal compound stent according to the present invention.Generally, compound stent 10 is a tubular stent comprising a pluralityof hoops 12 i-iii and 12′i-iii disposed axially along the length of thestent. Compound stent 10 comprises two component stents 20 and 20′joined together: a first component stent 20 having a plurality ofaxially-disposed individual hoops 12 i-iii and a connecting spine 22,and a second component stent 20′ having a plurality of axially-disposedindividual hoops 12′i-iii and a connecting spine 22′. The hoops of thefirst and second component stents are meshed together so that at leastone hoop of one component stent is positioned between axially adjacenthoops of the other component stent, as shown in FIG. 3. For example,hoop 12′_(i) is positioned between hoops 12 _(i) and 12 ii, hoop 12 iiis positioned between hoops 12′i and 12′ii, and so on.

As shown in FIG. 3, hoops 12 i-iii and 12′i-iii of stents 20 and 20′,respectively, are meshed with one another in a single hoop alternatingpattern. “Single hoop alternating pattern” as used herein means that thehoops alternate one hoop from stent 20, one hoop from stent 20′, and soon, traversing compound stent 10 in an axial direction. The alternatingpattern of stent 10 may be represented by a shorthand such as1:1:1:1:1:1, indicating that there are 6 hoops overall, alternating oneat a time. Other stents may be constructed in a two or othermultiple-hoop alternating pattern (2:2:2:2) or in a non-homogeneousalternating pattern (3:2:2:3, 1:2:1, etc.). Compound stents comprisingmore than two component stents may also be constructed.

Each hoop 12 and 12′ of stents 20 and 20′ comprises a pattern ofzig-zags between apices 13, as shown in FIGS. 1A-3. As shown in FIG. 3,abutting apices 13 of hoops 20 and 20′ may be connected together bysutures 14, as is well known in the art. As shown in FIGS. 1A and 1B,hoops 12 of stent 20 may be formed of a continuous wire 18 that windscircumferentially in a zig-zag pattern to make a first hoop 12 i, thenforms a spine member 21 i, then hoop 12 ii, and so on. The combinationof spine members 21 n between hoops 12 n and 12 n+1 collectively formspine 22, which wraps around the circumference of the stent in a helicalpattern. As shown in FIGS. 1A and 1B, spine 22 wraps about stent 20 in ahelical counter-clockwise fashion, as viewed from hoop 12 iii looking inthe direction of hoop 12 i.

Similarly, stent 20′, as shown in FIGS. 2A and 2B, comprises wire 18′wound into corresponding hoops 12′i-iii and connecting segments 21′i-iiof spine 22′ in what is essentially a mirror image of stent 20. As shownin FIGS. 2A and 2B, spine 22′ wraps about stent 20′ in a helicalclockwise fashion, as viewed from hoop 12′iii looking in the directionof hoop 12′i. As shown in FIG. 3, the two stents 20 (dark wires 18) and20′ (light wires 18′) come together to form compound stent 10. Althoughonly three hoops 12 or 12′ are shown on each stent 20 and 20′ toconserve space in FIGS. 1A-3, compound stent 10 may comprise as manyhoops as necessary to reach the desired length.

Wires 18 and 18′ may comprise a shape-memory material, such as nitinol.Although shown as single-wire, helical-spine stents in FIGS. 1A-3,component stents may be formed of compound stents having multiple wires,having non-helical spines or spines where the helical or other patternis broken into discrete sections between adjacent hoops rather thanaligned in a continuous spine, or having a spine that comprises aseparate wire from the wire comprising the hoops.

FIGS. 4A-4C are side views of a curved portion of compound stent 10 atthe inner radius of that curvature, showing how the apices 13 ofadjacent pairs of hoops 12 and 12′ may slip relative to one another andbecome interdigitated when compound stent 10 is flexed. As used herein,the term “interdigited” means that a portion of one hoop extends axiallyinto the axial length defined by an adjacent hoop. Thus, FIG. 4A shows acurved portion having a radius of curvature “R” that is greater than theradius of curvature for FIGS. 4B and 4C, with FIG. 4C illustrating thesmallest radius of curvature, or the most flexed state, of the threerelated figures.

The slippage direction of apices 13 of adjacent hoops 12 and 12′relative to one another may prevent torsional forces from developing incompound stent 10. The helical orientation of spines 22 and 22′ inopposite directions from one another may facilitate and direct suchslippage. The apices of hoops 12 tend to slip in the direction of arrow“B” and the apices of hoops 12′ tend to slip in the direction of arrow“C”, producing substantially a net zero torsional resultant force oncompound stent 10. Even if one or more hoops slip in the oppositedirection than expected, other hoops may compensate for suchmisdirection, maling the overall resultant still substantially zero.Providing a substantially zero resultant force is desirable so thatstent 10 may be flexed either at or after deployment to meet thetortuous curvature of the lumen in which it is implanted withouttorsional resistance forces potentially affecting the integrity of anyseal between the stent and the lumen. To achieve such a substantiallyzero resultant, each component stent having opposite helical spinespreferably has the same number of hoops.

Because spines 22 and 22′ circumscribe component stents 20 and 20′,respectively, in opposite rotational directions, the spines haveoverlapping sections 40 at regular intervals, as shown in FIG. 3.Overlapping section 40 may be a less flexible section than the remainderof the compound stent 10, and such overlaps may be integrated into theoverall stent design to provide flexibility and rigidity where desired.Where more than two component stents are meshed together to form acompound stent, overlapping sections may be distributed in a particularpattern to provide stiffness where desired. In particular, it may bedesirable to distribute overlapping sections so that each is spacedcircumferentially 180° from another. The more component stents meshedtogether, the more such overlapping sections created and the stiffer theresulting compound stent.

Abutting apices 13 of adjacent hoops 12 and 12′ are connected to oneanother with connectors 14, which may be sutures as shown in detail oval16 of FIG. 4B. During flexion of compound stent 10, sutures or otherconnectors 14 connecting interdigitated apices 13 may tend to develop anangular orientation with respect to longitudinal axis A of the compoundstent as shown in FIGS. 4A-4C. As shown, the angular orientation ofsuccessive connectors 14L and 14R along the length of compound stent 10may even alternate in opposing directions with respect to longitudinalaxis A. Thus, connectors 14L may become oriented from axis A pointing tothe left in the distal direction, whereas connectors 14R may becomeoriented from axis A pointing to the right in the distal direction.Slippage may still occur, however, without the sutures developing theparticular angular orientation as illustrated by sutures 14L and 14R inFIGS. 4A-4C.

Although illustrated herein with respect to compound stents comprisingonly two stents having hoops meshed in an alternating fashion with oneanother, the invention may also comprise a stent having more than twosuch stents with hoops so meshed. Where more than two such stents areinvolved, at least one of the stents may have a helical spine that isoriented oppositely from the others. For example, a three-stent compoundstent may comprise two clockwise spines and one counter-clockwise spine,or vice versa, whereas a four-stent compound stent may comprise twoclockwise and two counter-clockwise or three in one direction and one inthe opposite direction. The compound stent as disclosed herein may alsocomprise a liner of biocompatible graft material covering either theoutside of the stent, the inside of the stent, or both.

The present invention also comprises a process for manufacture of acompound stent as described and illustrated herein. Referring now toFIG. 5, there is shown a flowchart depicting an exemplary such process.The process comprises in step 100, creating a plurality of componentstents such as stents 20 and 20′ of FIGS. 1A-2B, each having a lengthand a plurality of individual hoops 12 i-iii and 12′i-iii respectively,axially disposed along their length and each having a connecting spine22 and 22′, respectively. Forming each component stent in step 100 mayfurther comprise step 100 a of winding a single wire, such as wires 18and 18′, on for example a mandrel, to form each hoop 12 i-iii and12′i-iii respective connecting spine members 21 i-ii and 21′i-ii betweenadjacent hoops, each set of collective connecting spine members forminghelically-oriented connecting spines 22 and 22′. Step 100 a may comprisecreating at least one component stent having a connecting spine with ahelical orientation opposite the helical orientation of a connectingspine in the another component stent, such as spine 22 that is helicalcounter-clockwise as compared to spine 22′ that is helical clockwise.Forming each hoop in step 100 a may further comprise in step 100 b,winding each hoop in a zig-zag pattern having apices 13.

Next, the process comprises in step 110, meshing the plurality ofcomponent stents together such that at least one hoop of one componentstent is positioned between axially adjacent hoops of another componentstent, such as hoop 12′i of stent 20′ meshed between hoops 12 i and 12ii of stent 20 in compound stent 10 of FIG. 3. The meshing step 110 mayfurther comprise step 110 a of distributing the hoops so that the apicesof adjacent hoops of the meshed component stents abut or areinterdigitated with one another, as is illustrated by abutting apices 13in FIG. 3. Furthermore, the meshing step 110 may comprise in step 110 bmeshing the plurality of component stents together such that theoppositely-orientated helical spines cross one another in at least onelocation along the compound stent, such as overlapping section 40 asshown in FIG. 3. Finally, in step 120, the process may further compriseconnecting at least some of the abutting or interdigitated apices, suchas sutures 14 and 14′ shown connecting apices 13 in FIG. 5.

Although illustrated and described herein with reference to certainspecific embodiments, the present invention is nevertheless not intendedto be limited to the details shown. Rather, various modifications may bemade in the details within the scope and range of equivalents of theclaims and without departing from the spirit of the invention.

What is claimed:
 1. A generally tubular intraluminal compound stentcomprising a plurality of component stents, each component stent havinga length and a plurality of individual hoops axially disposed along saidlength and connected by a connecting spine, at least a first connectingspine of a first component stent oriented in a first helical directionand a second connecting spine of a second component stent oriented in asecond helical direction opposite the first helical direction, saidcomponent stents meshed with one another such that at least one hoop ofone component stent is positioned between axially adjacent hoops ofanother component stent.
 2. The compound stent of claim 1 wherein eachcomponent stent comprises a single wire, each hoop comprising acircumferential winding of said wire, and said connecting spinecomprises at least one connecting spine member comprising an extensionof said wire between adjacent hoops.
 3. The compound stent of claim 1wherein each said hoop comprises a pattern of zig-zags having apices. 4.The compound stent of claim 3 wherein axially adjacent hoops of themeshed component stents are aligned such that the apices of axiallyadjacent hoops abut or are interdigitated with one another.
 5. Thecompound stent of claim 4 further comprising connectors connecting atleast some of said abutting or interdigitated apices.
 6. The compoundstent of claim 5 wherein said connectors are sutures.
 7. The compoundstent of claim 1 wherein each component stent comprises a shape-memorymaterial.
 8. The compound stent of claim 1 further comprising abiocompatible graft liner that covers said compound stent inside of thecompound stent, outside of the compound stent, or some combinationthereof.
 9. The compound stent of claim 1 consisting essentially of thefirst component stent having the first connecting spine and the secondcomponent stent having the second connecting spine.
 10. The compoundstent of claim 9 wherein the hoops of said first component stent areaxially interspersed with the hoops of said second component stent in analternating pattern.
 11. The compound stent of claim 10 wherein saidalternating pattern of hoops comprises a single hoop alternatingpattern.
 12. The compound stent of claim 11 wherein the first componentstent further comprises a first wire, each hoop of said first componentstent comprising a circumferential winding of said first wire, saidfirst connecting spine comprising at least one connecting spine membercomprising an extension of said first wire between adjacent hoops ofsaid first component stent, and wherein the second component stentfurther comprises a second wire, each hoop of said second componentstent comprising a circumferential winding of said second wire, saidsecond connecting spine comprising at least one connecting spine membercomprising an extension of said second wire between adjacent hoops ofsaid second component stent.
 13. The compound stent of claim 12 whereinthe first connecting spine is helically oriented in a clockwisedirection and the second connecting spine is helically oriented in acounter-clockwise direction.
 14. The compound stent of claim 13 whereineach said hoop of said first and second component stents furthercomprises a pattern of zig-zags having apices, the compound stentfurther comprising axially adjacent hoops of the meshed component stentsaligned such that the apices of axially adjacent hoops abut or areinterdigitated with one another and have connectors connecting at leastsome of said abutting or interdigitated apices.
 15. The compound stentof claim 14 wherein the connectors are sutures.
 16. A process formanufacture of a compound stent, the method comprising: a) creating aplurality of component stents, each component stent having a length anda plurality of hoops axially disposed along said length and connected bya connecting spine, at least a first connecting spine of a firstcomponent stent oriented in a first helical direction and a secondconnecting spine of a second component stent oriented in a secondhelical direction opposite the first helical direction; b) meshing saidplurality of component stents together such that at least one hoop ofone component stent is positioned between axially adjacent hoops ofanother component stent.
 17. The process of claim 16 wherein each saidhoop of said component stents further has a periphery comprising apattern of zig-zags having apices, the method further comprising meshingsaid component stents so that the apices of adjacent hoops of the meshedcomponent stents abut or are interdigitated with one another.
 18. Theprocess of claim 17 further comprising connecting at least some of theabutting or interdigitated apices with one another.
 19. The process ofclaim 16 further comprising in step (a) creating each said componentstent by winding a single wire circumferentially to form each hoop andextending connecting spine members between adjacent hoops, aligning saidconnecting spine members such that said connecting spine memberscollectively form a connecting spine oriented in a helical pattern. 20.The process of claim 19 wherein in step (b) meshing said plurality ofcomponent stents together further comprises crossing said first spineover said second spine in at least one location along said compoundstent.
 21. The stent of claim 9 wherein the first component stent andthe second component stent have a same number of hoops.
 22. A generallytubular intraluminal compound stent comprising a plurality of componentstents, each component stent having a length and a plurality ofindividual hoops axially disposed along said length and connected by aconnecting spine, at least a first connecting spine of a first componentstent oriented in a first helical direction and a second connectingspine of a second component oriented in a second helical directionopposite the first helical direction, each hoop comprising acircumferential member, said component stents meshed with one anothersuch that at least one hoop of one component stent is positioned betweenaxially adjacent hoops of another component stent.
 23. A process formanufacture of a compound stent, the method comprising: a) creating aplurality of component stents, each component stent having a length anda plurality of hoops axially disposed along said length and connected bya connecting spine, each hoop comprising a circumferential member, andat least a first connecting spine of a first component stent oriented ina first helical direction and a second connecting spine of a secondcomponent oriented in a second helical direction opposite the firsthelical direction; and b) meshing said plurality of component stentstogether such that at least one hoop of one component stent ispositioned between axially adjacent hoops of another component stent.